<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8" />
    <title>Document</title>
    <script src='lib/webgl-utils.js'></script>
    <script src='lib/webgl-debug.js'></script>
    <script src='lib/cuon-utils.js'></script>
    <script src="lib/cuon-matrix.js"></script>
</head>
<body onload="main()">
<canvas id="mybox" width="500" height="500">
    请更换新版浏览器查看效果!
</canvas>
<script >
    let VSHADER_SOURCE=`
    attribute vec4 a_position;
    uniform mat4 u_xformMatrix;
    void main(){
        gl_Position=u_xformMatrix * a_position;
    }`;
    let FSHADER_SOURCE=`
    void main(){
        gl_FragColor=vec4(1.0,0.3,0.3,1.0);
    }`;
    let ANGLE=90;


    function main(){
        let canvas=document.getElementById('mybox')
        let gl=getWebGLContext(canvas)
        if(!initShaders(gl,VSHADER_SOURCE,FSHADER_SOURCE)){
            console.log('初始化shader失败');
            return;
        }
        let n=initVertexBuffers(gl)
        if(n<0){
            console.log('设置顶点位置失败')
            return;
        }
        let xformMatrix=new Matrix4();
        xformMatrix.setRotate(ANGLE,0,0,1);
        let u_xformMatrix=gl.getUniformLocation(gl.program,'u_xformMatrix')
        gl.uniformMatrix4fv(u_xformMatrix,false,xformMatrix.elements)

        gl.clearColor(0.0,0.0,0.0,1.0);
        gl.clear(gl.COLOR_BUFFER_BIT);
        gl.drawArrays(gl.TRIANGLES,0,n)



    }

    function initVertexBuffers(gl){
        let vertices=new Float32Array([0.0,0.3,-0.3,0.0,0.3,0.0])
        let n=3;
        let vertexBuffer=gl.createBuffer();
        gl.bindBuffer(gl.ARRAY_BUFFER,vertexBuffer);
        gl.bufferData(gl.ARRAY_BUFFER,vertices,gl.STATIC_DRAW);
        let a_position=gl.getAttribLocation(gl.program,'a_position');
        gl.vertexAttribPointer(a_position,2,gl.FLOAT,false,0,0);
        gl.enableVertexAttribArray(a_position);
        return n;
    }


</script>

</body>
</html>